Island Drive Bridge

Prime consultant: Cook Engineering

The Island Drive Bridge completed in November 2002 links mainland Thunder Bay across the Kaministiquia River to two large islands that are the site of major industries, including an electrical generating station and a coal-handling terminal. The islands are the hub of fuel distribution for northwestern Ontario.

The only access to the islands used to be via an aging Bascule Bridge built in the early 1900s, which has since been closed to vehicular traffic. The city asked for design/build proposals for a new crossing downstream that would consist of a 100-metre fixed bridge, 100-metres of filled river causeway and 400 metres of approach embankments.

Cook Engineering’s alternative proposal was for a bridge that spans the full width of the river and has integral abutments. Measuring 234 metres long, the completed structure is the longest integral abutment bridge in Canada.

The integral abutment concept resulted in $300,000 capital savings compared to a conventional abutment bridge. The design also eliminates the need for expansion joints, which can require ongoing maintenance, and it minimized the environmental impact. A project that involved many stakeholders was completed six months ahead of schedule and within the $11 million budget.

Allowing for movement

The 12-metre wide superstructure consists of 1.8-m deep twin steel box girders acting compositely with a reinforced high performance concrete deck. The bridge has three piers and four continuous spans: two are 52.5 metres and two are 64.5 metres.

The bridge has an asymmetrical vertical curve to accommodate approaches to a railway crossing on the mainland. Maximum tangent grades of 5% were used. The bridge is too low to allow tugboats to navigate the river, but the city decided that rather than raising the structure and hence raising the costs, it was more economical to have the tugboats shorten their masts at the city’s expense — which was successfully done.

The abutments have to move as the deck expands during hot weather and contracts during cold weather. The engineers decided to encase the upper portions of the foundation piles in oversize steel caissons. In a departure from common practice, the caissons were not filled with sand in order to allow the structure to move. However, at the north abutment the water table was high and above the frost line, which meant that during the winter, water in the caisson could freeze and resist the movement of the piles. To solve the problem, an extremely low-stiffness, low-absorption rebounding foam plug was placed inside the caissons to displace much of the water. The area was also covered by insulation foam for extra protection.

Relatively weak clays at the south abutment added complications. Given the embankment’s massive size and weight (it rises about 10 metres above the original grade), there would be excess pressure on the clay beneath. To speed up the process of consolidating those clays and meet the fast track schedule it was decided to excavate six metres of undesirable clays below the embankment and backfill the excavation with granular material. The embankment was then constructed in two stages, with six months in between to allow the soils to settle.

Compared to the causeway concept, this solution minimized disturbance to the environment and reduced the impact on the foundations of a nearby hydro high-voltage transmission tower.

A wetland of 0.6 hectares was added on the north shoreline adjacent to the bridge, while the fish habitat lost due to the construction was more than compensated for by adding rock protection on the shores and around the pier caissons. The net gain was approximately three times the lost riverbed area, and should result in increased fish and terrestrial bio-diversity.

Client/project management: City of Thunder Bay

Prime consultant, road, bridge and wetland design:

Cook Engineering (Primo Scalzo, P.Eng., Dr. Kaz W. Simbeya, P.Eng., Frank.M. Adams, P.Eng., Trina Rawn, B.Sc.,

Toby Kukko, P Eng.)

Other consultants: Dr. Walter Dilger, Ph.D. (specialist);

DST Consulting Engineers (geotechnical); North Shore

Environmental Services (fisheries); Sean Randall (artist);

Werner Schwar (landscape); Adamson Consulting

(erosion and sediment)

Design-builder: Bruno’s Contracting

Sub-contractor: MLA Northern Contracting